The present invention relates to an electroconductive roller provided in a device used as a process equipment in an image forming apparatus and testing method and testing device for testing the surface condition of the electroconductive roller used in the image forming apparatus, and more particularly, to testing method and testing device for testing the surface condition of the electroconductive roller which influences the quality of an image formed by the image forming apparatus.
Conventionally, as a device used as a process equipment in an image forming apparatus such as an electronic copying machine or a laser-beam printer, a developing device which supplies toner onto a photosensitive drum so as to develop (visualize) an electrostatic latent image formed on the photosensitive drum is known. In recent years, some image forming apparatuses, which use non-magnetic single-component toner, employ a developing roller such as an electroconductive roller as a part in the developing device to transfer the toner.
The developing roller is formed by, e.g., providing a roller body of electroconductive rubber on the outer periphery of a metal core, and coating the outer peripheral surface of the roller body with electroconductive resin. In this construction, the toner is charged and adsorbed by the friction between the outer peripheral surface and the toner, and the toner is transferred onto the outer peripheral surface of the photosensitive drum via fine irregularities of the outer peripheral surface of the developing roller, by rotation of the developing roller.
In the conventional art, the surface roughness (including so-called "waviness") of the developing roller has been widely noticed as a factor to influence the quality of an image formed by the image forming apparatus. The quality of the developing roller has been managed based on how to maintain the surface roughness within a predetermined range; in other words, the quality management has been made such that the developing roller having surface roughness out of the predetermined range is discarded as a bad (no good) product.
In this manner, to test the surface roughness of the developing roller, based on the Japanese Industrial Standard (JIS), a testing needle must be brought into contact with the outer peripheral surface of the developing roller, which might damage the peripheral surface. In this testing, even if the test result is "good", a developing roller with a damaged surface must be discarded as a defective product.
Further, the surface roughness test takes a very long time. In a case where the moving speed of the testing needle is set to 0.3 mm/sec and the outer peripheral surface of the developing roller is .phi.16 mm, if the test is performed on the entire outer peripheral surface of the developing roller, the testing length is about 50.24 mm, and it takes about 3 minutes to complete this test. In practice, it is impossible to test all the developing rollers from the viewpoint of productivity, and improvement of this testing method is required.
On the other hand, to avoid damaging the outer peripheral surface of a developing roller, the developing roller is installed in an image forming apparatus without the above surface roughness test, and an image of "solid black", for example, is formed on a sheet by actually performing image forming process of the apparatus, and the density unevenness of the image is judged (so-called image test by actually using image forming apparatus). However, in this test, if it is determined that the image quality is degraded due to a bad developing roller, the developing roller must be replaced with a new developing roller, and thereafter, the same test must be performed on the apparatus again. In this manner, the efficiency of this test is very low and it must be improved.